1. Technical Field
The present invention relates to a clear ink composition, and especially relates to a clear ink composition, which exhibits excellent fixability, enables a record with excellent gloss and color development to be produced, and enables excellent printing stability to be exhibited after passage of time, even in printing on various recording media, particularly a recording medium that exhibits low water absorbability, such as synthetic paper or actual printing paper.
2. Related Art
An ink jet recording method is a printing method in which ink droplets are ejected and then adhere to a recording medium such as paper to perform printing. In recent years, the ink jet recording method has been innovatively developed and has therefore come to be used even in the field of highly precise printing which has been enabled only by silver halide photography and offset printing. An ink jet recording ink has been accordingly developed, which can be applied to a recording medium exhibiting high gloss equal to that of photographic paper, art paper, or the like that has been used in the field of the silver halide photography and the offset printing, namely specialty paper, with the result that an image with gloss equal to that in silver halide photography can be formed. In addition, an ink jet recording ink has been developed, which can be used to provide print quality equal to that of the silver halide photography even in the case where plain paper is used.
In order to form a high-quality image, a technique has been proposed, in which an ink composition and a clear ink composition not containing a colorant are brought into adhering to a recording medium to perform printing. A technique is proposed, for example, in JP-A-2003-335058, in which an ink composition containing a colorant is used to form an image and in which a clear ink composition is then brought into adhering to the image.
Meanwhile, in recent years, a technique for forming an image from digital data has been widely used. Desktop publishing (DTP) is therefore being widely used particularly in the field of printing. Even in the case of DTP printing, color proofs are prepared in advance for the purpose of checking the gloss and color of actually produced prints.
An ink jet recording technique is used to output the color proofs, and a print needs to be formed in the DTP so as to have color that is stably reproduced. In general, specialty paper for ink jet recording is therefore used as recording medium.
The specialty paper for ink jet recording is designed so as to exhibit gloss and color equivalent to those of an output that is actually printed on actual printing paper. A material for the specialty paper is appropriately selected depending on the type of actual printing paper. However, production of the specialty paper which can be used for all types of actual printing paper leads to the increased production costs. For color proof applications, a demand accordingly arises, in which the actual printing paper, rather than the specialty paper, is desired to be used in ink jet printing. If final proofs can be directly printed on the actual printing paper rather than the specialty paper by ink jet printing, proofreading costs can be significantly reduced. In recent years, synthetic paper which is prepared as a result of forming a mixture of polyethylene or polyester and an inorganic filler or the like into a film has been widely used in the field of printing and has attracted attention as an environmentally friendly material with good recyclability.
The actual printing paper is coated paper having a surface on which a coating layer is formed for absorbing an oil-based ink and is characterized in that the coating layer has low ink absorbability. In the case of using an aqueous pigment ink which is commonly used in ink jet printing, a blur and an aggregation spot may be therefore caused in an image owing to poor permeability of the aqueous pigment ink to the recording medium (actual printing paper).
In order to solve this problem, for example, JP-A-2005-194500 discloses a pigment ink which contains a polysiloxane compound as a surfactant and an alkanediol such as 1,2-hexanediol as a dissolution aid to reduce a blur and to provide excellent gloss on specialty paper. In addition, JP-A-2003-213179, JP-A-2003-253167, and JP-A-2006-249429 disclose techniques in which addition of glycerin, a diol such as 1,3-butanediol, or a triol alcohol solvent such as pentanetriol to ink contributes to controlling the permeability of ink to a recording medium and therefore serves to form a high-quality image.
JP-A-2009-209338 discloses an ink composition which contains a colorant, water, water-insoluble alkanediol, water-soluble 1,2-alkanediol, dialkylene glycol, and a surfactant and which can be therefore used to produce a high-quality record without the occurrence of printing defect in printing on a recording medium exhibiting low water absorbability. JP-A-2009-297924 discloses a clear ink composition which at least contains a water-insoluble alkanediol, a water-soluble alcohol, water, and fine polymer particles without addition of a colorant and which therefore exhibits excellent fixability and can be used to produce high-quality record without the occurrence of printing defect. However, an ink composition has not been developed yet, which exhibits excellent fixability, enables a record with excellent gloss and color development to be produced, and enables excellent printing stability to be exhibited after passage of time, even in printing on various recording media, particularly a recording medium with low water absorbability, such as synthetic paper and actual printing paper. Such an ink composition has been therefore desired to be developed.
The inventors have found the following: a clear ink composition is prepared so as to contain a water-insoluble alkanediol, a water-soluble alcohol as a dissolution aid for dissolving the water-insoluble alkanediol (hereinafter simply referred to as “water-soluble alcohol”, where appropriate), water, fine polymer particles at least containing polyolefin, and a fluorene resin without addition of a colorant; and by virtue of such a clear ink composition, excellent fixability can be exhibited, a record with excellent gloss and color development can be produced, and excellent printing stability can be exhibited after passage of time, even in printing on various recording media, particularly a recording medium that exhibits low water absorbability, such as synthetic paper or actual printing paper. Embodiments of the invention are provided on the basis of this finding.